Fatty acid esters of N-methyl-N,N,N-trihydroxyethyl ammonium methyl sulfate are cationic tensides. The production of these esters can take place according to various methods known from the literature.
U.S. Pat. No. 3,915,876 describes a synthesis method for N-methyl-N,N-di-(.beta.-C.sub.14 -C.sub.18 -acyloxyethyl)-N-.beta.-hydroxyethyl ammonium methyl sulfate starting with triethanolamine and fatty acid methyl esters in a molar ratio of 1:2, by transesterification in the presence of sodium methylate as a catalyst, under mild conditions, and subsequent quaternization with dimethyl sulfate. Particularly light-colored products are obtained.
DE 37 10 064 contains the conversion of glycerin tristearate with triethanolamine. In this transesterification, a product mixture of about 50% triethanolamine stearates and 50% glycerin stearates, as well as free glycerin, is obtained. After its quaternization with methyl chloride, a mixture of cationic tenside and the by-products mentioned, which are not separated off, is obtained.
DE 37 20 332 claims a method for the production of fatty acid esters of N-methyl-N,N,N-trihydroxyethyl ammonium methyl sulfate by direct esterification of triethanolamine with fatty acid in the presence of catalytic amounts of fatty acid methyl esters and subsequent quaternization with dimethyl sulfate.
The cationic tensides are generally diluted with up to 25% isopropanol or other alcohols or diols of low molecular weight in order to make them easier to handle.
The products which can be produced according to the prior methods discussed above are particularly useful as fabric softeners with good ecotoxicological properties. In this area of technology it is common for emulsions consisting of cationic tensides, dispersion agents, perfume and pigments as well as other components, to get into water.
The cationic tenside is generally present in the form of micro-dispersed droplets, which are not allowed to coalesce, since this would result in separation of the product into several phases. In the formulation of a fabric softener, it is therefore of great importance that the emulsion be stabilized. The current trend towards so-called "fabric softener concentrates" with an active substance content of 15-25% presents the formulator with significant viscosity problems.
In spite of the high content of cationic tensides, the emulsion must be made as non-viscous as possible, because this achieves not only better pourability, but also a more uniform distribution of the active substance in the rinse, combined with an increased softening effect. To reduce viscosity, various dispersion agents are added.
U.S. Pat. No. 3,915,867 describes that N-methyl-N,N-di-(.beta.-C.sub.14 -C.sub.18 -acyloxyethyl)-N-.beta.-hydroxyethyl ammonium methyl sulfate forms self-emulsifying fabric softeners and that no emulsifiers, such as non-ionic tensides, for example, are required. The softening properties of an 8%, i.e. dilute, emulsion are described, without viscosity information. The active substance was produced on the basis of fatty acid methyl esters.
EP 0 040 562 discloses 20% fabric softener concentrates with N-methyl-N,N-di-(.beta.-C.sub.14 -C.sub.18 -acyloxyethyl)-N-.beta.-hydroxyethyl ammonium methyl sulfate as the cationic active substance. As dispersion agents, 10 to 67% non-ionic tensides, with reference to the cationic tenside, e.g. fatty alcohol oxyethylates, are used. The products have viscosities from 100-900 mPa.s and must be adjusted to viscosities of 40-80 mPa.s before use, by being diluted with water.
L. Godefroy and H. Hein, Seifen-Ole-Fette-Wachse [Soaps-Oils-Fats-Waxes] 115, 3 (1989) use dialkyl ammonium esters on the basis of partially hydrogenated tallow as a fabric softener component and achieve emulsions at 30-60 mPa.s by adding 2.8 to 3.6% N-methyl-N,N,N-trihydroxyethyl ammonium methyl sulfate, with reference to the cationic tenside, as the "fluidizing agent" to liquefy concentrated (16.7-27.8%) emulsions. Without this liquefier, a 5.56% emulsion already has a viscosity of 60-80 mPa.s at 20.degree. C.
DE 37 20 331 eliminates the disadvantage of high viscosities with a combination of the di-fatty acid ester of N-methyl-N,N,N-trihydroxyethyl ammonium methyl sulfate with 10 to 90% of a second cationic component, e.g. di-tallow fatty acid alkylimidazolinium methyl sulfate, di-stearyl dimethyl ammonium chloride, N-methyl-N-triethoxy-N,N-bis-[2-(tallow fatty amido)-ethyl]ammonium methyl sulfate, and optimally with a dispersion agent, e.g. a mixture of oleylaminoxethylates and oleic acid. The preparation of such formulations requires additional effort for storage and mixing.
These dispersion agents necessary for fabric softeners represent a significant disadvantage in terms of application technology.
It was therefore the task of the present invention to produce aqueous emulsions that have a low viscosity, are self-emulsifying, stable, concentrated and contain fatty acid esters on a nitrogen basis.